The present invention relates to a battery device including a plurality of battery units, such as battery cells, battery modules, or battery packs, incorporated in a desired enclosure and adapted for use as a power source for an electric vehicle, for example.
Various attempts have been made to develop a battery device (battery assembly) for use as a driving energy source for an electric vehicle or the like, in which a plurality of battery units are connected in series and/or parallel with one another. Each battery unit is provided as a battery cell (single battery), a battery module formed of a plurality of battery cells connected in series with one another, or a battery pack including the battery module and an electronic circuit, such as a charge/discharge control circuit, incorporated therein.
In the case where a battery device is constructed by using a plurality of cylindrical battery modules 1 each comprised of battery cells connected in series with one another by welding or the like and externally covered by a protective heat-shrinkable tube, for example, these battery modules 1 are generally arranged at given spaces in a matrix in a box-shaped enclosure 2, as shown in FIG. 1. In this case, the enclosure 2 serves to receive and hold the battery modules 1 therein and to define therein an airflow path through which air (coolant or cooling medium) flows along the respective peripheral surfaces of the individual battery modules 1. In the battery device specifically shown in FIG. 1, the battery modules 1 are cooled by a forced air flow flowing between one and the other end openings of the enclosure 2 and produced by a fan 3 attached to the one end opening.
More specifically, as shown in the schematic plan view of FIG. 2A, the battery modules 1, e.g., 18 in number, are arranged at given spaces in the airflow direction in a 3-column, 6-row rectangular matrix in the enclosure 2. Air introduced through an opening 2a of the enclosure 2 is caused to flow along the respective peripheral surfaces of the battery modules 1 in the direction of arrangement thereof via the spaces between the battery modules 1 and between the wall of the enclosure 2 and the battery modules, whereby the battery modules 1 are cooled.
Although air (coolant) is forced to flow in the enclosure 2 in the above manner to cool the battery modules 1, there inevitably occur differences in battery temperature between the battery modules 1. The temperature differences may cause a variation in charge/discharge state and individual differences in battery life, residual battery capacity, etc. between the battery modules 1, thus arousing problems on quality and stability.
In order to minimize a temperature increase attributable to a charge or discharge action of the battery modules 1, thereby lessening the temperature differences between the battery modules 1, the rate of airflow produced by a fan 3 may be increased. Since pressure loss increases as the airflow rate increases, the fan 3 is expected be of a high-power, large-sized type, so that the battery device is large-scaled, and besides, there is a problem that constitutes a hindrance to energy conservation.
The present invention has been contrived in consideration of these circumstances, and its object is to provide a simple-construction battery device, capable of reducing battery temperature differences between a plurality of battery units arranged in an enclosure and enjoying improved quality and operation stability.
Another object of the present invention is to provide a simple-construction battery device in which a plurality of battery units arranged in an enclosure can be uniformly cooled without regard to their locations.
A further object of the present invention is to provide a battery device having a structure such that a plurality of battery units can be efficiently cooled by means of air that is introduced into an enclosure and caused to flow along the respective peripheral surfaces of the battery units.
The present invention is based on the following findings. In a battery device having therein a plurality of battery units arranged in rows at given spaces in an enclosure and a coolant flow path extending around the battery units in the direction of arrangement thereof, as shown by way of example in FIG. 2A, the temperature of air (coolant) that flows in the direction of arrangement of the battery units (battery modules) increases from the upstream side to the downstream side, as shown in FIG. 2B. Further, the ability of heat transfer (cooling efficiency) between air and the battery modules in the individual rows is low in the first row or on the uppermost-stream side of the airflow path and higher in a second row and its subsequent rows. In association with the coolant temperature and the cooling efficiency, the battery temperatures of the battery modules are low in the second and third rows and high in the first row.
Thus, the present invention is based on findings that the ability of heat transfer (cooling efficiency) between the coolant and the battery modules in the individual rows, including a plurality of battery units arranged in a multistage fashion, is associated intimately with turbulence of the coolant flow, and the heat transfer ability of the coolant flow for cooling the battery units increases in the second and subsequent rows with the increase in distance from the first row since the coolant flow is disordered by the battery units on the upper-stream side. In particular, the present invention is based on findings that the increase, observed between the first and second rows, of the heat transfer ability for the battery units is much greater than the increase of the ability of heat transfer between other rows, and that the coolant flows more positively from the first row to the second row than between other rows.
In a battery device according to the present invention, one or more turbulence accelerators, formed of dummy battery units, battery components such as capacitors, or dedicated cylindrical bodies, are provided in a position on the upper-stream side of the battery units disposed on the uppermost-stream side of the coolant flow path. Coolant flows (airflows) guided to the respective peripheral surfaces of the first-row battery units are disordered by the turbulence accelerators, thereby providing a battery device in which the heat transfer ability (cooling efficiency) for the first-row battery units is enhanced.
According to the present invention, moreover, there is provided a battery device constructed so that the battery units located in a plurality of rows on the upper-stream side of the coolant flow path are arranged in an in-line rectangular matrix, and the battery units located on the lower-stream side of the coolant flow path are arranged in a staggered triangular matrix, whereby the coolant flows can be disordered to a higher degree on the lower-stream side than on the upper-stream side so that the coolant temperature on the upper-stream side increases, and the heat transfer ability (cooling efficiency) for the battery units located on the lower-stream side is enhanced correspondingly.
According to the present invention, furthermore, there is provided a battery device constructed so that the arrangement pitch, as viewed in the coolant flow direction, of the battery units on the upper-stream side of the coolant flow path is shorter than the arrangement pitch, as viewed in the coolant flow direction, of the battery units on the lower-stream side of the coolant flow path. In other words, there is provided a battery device constructed so that the coolant temperature on the lower-stream side is increased by widening the arrangement pitch of the battery modules on the lower-stream side, whereby the heat transfer ability (cooling efficiency) on the lower-stream side is enhanced correspondingly.
According to the present invention, moreover, there is provided a battery device constructed so that an enclosure surrounding the battery units arranged in rows and defining the coolant flow path is provided, the coolant flow path having a sectional area which is reduced from the upper-stream side to the lower-stream side, whereby the flowing speed of the coolant on the lower-stream side is increased so that the coolant temperature on the lower-stream side is increased to enhance the heat transfer ability (cooling efficiency) correspondingly.
According to the present invention, moreover, there is provided a battery device constructed so that the wall of an enclosure surrounding the battery units arranged in rows and defining the coolant flow path is formed with auxiliary coolant intake ports through which the coolant is introduced into intermediate portions of the coolant flow path, whereby the coolant temperature on the lower-stream side is lowered, and the heat transfer ability (cooling efficiency) on the lower-stream side is enhanced by utilizing pressure differences in the coolant.
According to the present invention, furthermore, there is provided a battery device constructed so that the enclosure is provided with a bypass channel through which the coolant is introduced into the auxiliary coolant intake ports, whereby a low-temperature coolant can be securely introduced into the region on the lower-stream side.
According to the present invention, moreover, there is provided a battery device constructed by combining the above-described structures.
Preferably, according to the present invention, the sectional area of the coolant flow path defined by the enclosure is narrowed on the lower-stream side by reducing the width of the enclosure, surrounding the battery units arranged in rows and defining the coolant flow path, from the upper-stream side to the lower-stream side, and the battery units in the individual rows in the coolant flow direction are arranged in regions of the enclosure at which regions the width of the enclosure is divided equally. Further preferably, according to the present invention, a dummy for keeping the width of the coolant flow path around the individual battery units substantially uniform is provided in the region for the staggered triangular arrangement of the battery units, whereby the coolant flow path can be prevented from being undesirably widened by the staggered triangular arrangement.